# Third Palatal Rugae as Stable Landmarks for Intraoral Models' Superimposition in Extraction Cases: A Retrospective Cohort Study

## TL;DR

This study shows that using the third palatal rugae as landmarks for digital models is reliable for tracking dental changes after tooth extraction and incisor movement.

## Contribution

Validates third palatal rugae as stable landmarks for superimposing intraoral models in extraction cases.

## Key findings

- The mean differences between methods were less than 0.2 mm in all comparisons.
- No statistically significant differences were found between intraoral-scan and CBCT measurements.
- Third palatal rugae superimposition is valid for 3D evaluation of short-term dental changes.

## Abstract

To validate the third palatal rugae as stable reference landmarks for the superimposition of maxillary digital models in premolar extraction cases.

Maxillary intraoral scanning digital models of 22 extraction patients, obtained before (T0) and after approximately 4 months of incisor retraction (T1), were superimposed using the automated best‐fit of the third palatal rugae and palatine raphe. Voxel‐based registration of CBCT scans served as the gold standard. Point‐to‐point displacements between T0 and T1 of the central incisors and cuspids were calculated for both methods.

The mean differences (mismatch) between methods in the combined vertical and horizontal perspectives of the central incisors were 0.08 mm (right) and 0.12 mm (left), respectively. For the cuspids, the mean 2D differences were 0.02 mm (right) and 0.07 mm (left). The pure horizontal displacement differences of the maxillary central incisors were 0.13 mm (right) and 0.04 mm (left). For the cuspids, the differences were: 0.05 mm (right) and 0.03 mm (left). No statistically significant differences were found between the intraoral‐scan and CBCT measurements for either the central incisors or cuspids after maxillary superimpositions. The differences between the two methods were smaller than 0.2 mm in all comparisons.

Digital superimposition of the third palatal rugae of models obtained with intraoral scans is a valid method for the 3D evaluation of the short‐term (4‐month) dental changes in the anterior region of the maxilla in cases of premolar extraction followed by incisor retraction.

ClinicalTrials.gov: NCT03089996 and NCT05281588